1. Field of the Invention
The present invention relates to a wireless communication system and a communication method using the same.
2. Description of the Related Art
Wireless communication systems are aimed at providing mobile stations with communication services beyond the boundaries of wired communication systems. A typical example of a wireless communication system is a cellular mobile communication system for providing voice services. A code division multiple access (CDMA) method is commonly used in the cellular mobile communication system so as to identify users. In addition to the CDMA method, a time division multiple access (TDMA) or a frequency division multiple access (FDMA) method may also be used.
In line with recent development in technologies, cellular systems have evolved to provide data services, as well as voice services. Particularly, efforts have been made to provide faster data services in cellular systems. This has resulted in development of various types of relevant methods, including orthogonal frequency-division multiplexing (OFDM). As such, an increase in data transmission rate is an important issue in current and future wireless communication systems. In order to increase the data transmission rate in wireless communication systems, frequencies must be reused properly, and interference between transmitted signals must be adjusted appropriately.
In addition to cellular mobile communication systems, there also exist other types of wireless communication systems, including a wireless local area network (LAN) system, which has been extended from a wired LAN system, an ad hoc network system, in which mobile stations replace hosts and perform communication services, and a wireless broadband (WiBro) system, in which orthogonal frequency resources are divided and used. Each wireless communication system has and is distinguished by its own wireless communication method. In other words, the type of a system depends on the wireless communication method adopted by the system.
Furthermore, each wireless communication system runs independently. This means that different types of wireless communication systems are not compatible with each other. Consequently, when a subscriber of a system wants to replace it, he must additionally purchase and use a mobile station dedicated to a desired system. This burdens the user with additional expenditure and inconvenience resulting from replacement of the mobile station.
In attempt to solve these problems, methods for using mobile stations in different systems, as well as methods for providing corresponding services, have been proposed. Particularly, methods for handing over mobile stations between different systems have been studied.
Future wireless communication systems are believed to be ubiquitous. In an ubiquitous systems, information technology is available everywhere, particularly at home, in automobiles, and even on top of a mountain. In addition, increased number of computer users connected to networks expands the scale and range of the information technology industry. However, such a ubiquitous environment cannot be realized until different networks are compatible with each other.
However, a method for providing compatibility between different types of wireless communication systems has been neither developed nor proposed yet. Therefore, a hybrid wireless communication system needs to be developed for the sake of a ubiquitous environment. In addition to compatibility, it is desired to devise a method for efficiently using resources of different wireless communication systems. Particularly, a decrease in data transmission rate must be avoided in a hybrid wireless communication system, in addition to guaranteeing a real time voice service. In order to maintain a high data transmission rate in a hybrid wireless communication system, a method for efficiently re-using frequencies is necessary, and so is a method for preventing interference. A stable voice service must also be provided.